Compounds containing 1-oxa-3-aza tetraline groups and their prepolymers (hereafter called "oxazene resins" by convenience) are known, for example form Swiss Patents Nos. 574,978, 579,113 and 606,169. They can be obtained, for example, from phenols by reaction with formaldehyde and an amine, according to formula (A): ##STR1## wherein R is, for example, hydrogen, halogen, alkyl or alkoxy, and R' is an aliphatic or aromatic group.
However, they can also be prepared by other processes leading to similar products.
In contrast to other known condensation reactions of phenols, amines and formaldehyde, in the reaction outlined above phenolic OH groups are consumed, it is thereby possible, according to the formula (A) hereinabove, to determine the amount of the synthesized 1-oxa-3-aza tetraline groups from the analytic determination of the said OH groups in the reaction mixture.
Prepolymers of 1-oxa-3-aza tetraline group containing compounds are also useful in preparing said oxazene resins. Since some of the 1-oxa-3-aza tetraline groups may react during polymerization, these prepolymers may contain a fewer number of said 1-oxa-3-aza tetraline groups than provided by the monomers used to form such prepolymers. It is essential, however, that the intermediately formed or hypothetic monomer reaction product does in fact contain 1-oxa-3-aza tetraline groups. This can easily be calculated by a person skilled in the art from the functionality. An oxazene resin, or its prepolymer, useful in accordance with the invention is, for instance, formed if the molar ratio is kept within the limits defined in Swiss Patent No. 606,169.
Phenol and phenol derivatives, respectively, as well as amines and formaldehyde are used as starting or basic materials for preparing the oxazene resin.
Preferably, for the present invention, 1-oxa-3-aza tetraline group containing compounds are used which are formally derived from a phenol and an amine, one of said components being more than monofunctional.
Examples of phenols that can be used include:
Monovalent phenols, such as phenol, m and p-cresol, m- and p-ethyl phenol, m- and p-isopropyl phenol, m- and p-isopropyloxy phenol m- and p-chloro phenol and betanaphthol. Meta-substituted phenols are preferred, since they do not include any blocked reactive positions. PA0 Bivalent phenols, such as 4,4'-dihydroxydiphenylmethane, 3,3'-dihydroxy-diphenylmethane, 2,2'-bis-(4-hydroxyphenyl)-propane, 4,4'-dihydroxy-stilbene, hydroquinone, pyrocatechol, and resorcin. PA0 Low-condensed phenol formaldehyde novolak resins, eventually mixed with a phenol. PA0 Examples of amines that are particularly useful include: PA0 Aniline, o-, m- and p-phenylene diamine, benzidine, 4,4'-diaminodiphenyl methane, cyclohexylamine, ethylenediamine, and propylenediamine. PA0 (a) a resin component comprising at least one thermically curable 1-oxa-3-aza tetraline group containing compound; and of PA0 (b) a second component comprising at least one flame retardant selected from the group consisting of:
Polymeric resins on the basis of 1-oxa-3-aza tetraline group containing compounds are resistant to high temperatures of more than 200 .degree. C., and up to more than 300 .degree. C. The flame resistance, despite the fact that it compares favorably with that of other polymeric resins resistant to high temperatures, such as for instance epoxy resins is still not sufficient for many uses. The attempt to improve said flame resistance by incorporating of halogen would result in the drawback that highly toxic gases of combustion are formed in case of fire.
It is known to improve the flame resistance of some inflammable polymeric resins, such as epoxide resins and unsaturated polyester resins, by addition of a flame retardant which is not mixable with the polymeric resin. However, for achieving self-extinguishing properties such a high amount of additive is necessary, for instance 200 phr and more, that the good mechanical properties of these resins are lost.
As usual, in the present specification "phr" means "parts by weight of additive per 100 parts by weight of resin".
Therefore, such systems are practically unsuitable for preparing highly reinforced polymeric resins. Difficultly inflammable phenolic resins are also out of the question for said use, since, per se, they already show much lower mechanical properties. In spite the serious toxicological doubts, no satisfying alternative to halogenated systems was found so far.